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Freely decaying, homogeneous turbulence generated by multi-scale grids

Published online by Cambridge University Press:  19 May 2011

P.-Å. KROGSTAD  and
P. A. DAVIDSON
P.-Å. KROGSTAD*
Affiliation:
Department of Energy and Process Engineering, Norwegian University of Science and Technology, N-7491 Trondheim, Norway
P. A. DAVIDSON
Affiliation:
Department of Engineering, University of Cambridge, Cambridge CB2 1PZ, UK
*
†Email address for correspondence: per.a.krogstad@ntnu.no
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Abstract

We investigate wind-tunnel turbulence generated by both conventional and multi-scale grids. Measurements were made in a tunnel which has a large test section, so that possible side wall effects are very small and the length ensures that the turbulence has time to settle down to a homogeneous shear-free state. The conventional and multi-scale grids were all designed to produce turbulence with the same integral scale, so that a direct comparison could be made between the different flows. Our primary finding is that the behaviour of the turbulence behind our multi-scale grids is virtually identical to that behind the equivalent conventional grid. In particular, all flows exhibit a power-law decay of energy, u2 ~ t−n, where n is very close to the classical Saffman exponent of n = 6/5. Moreover, all spectra exhibit classical Kolmogorov scaling, with the spectra collapsing on the integral scales at small k, and on the Kolmogorov microscales at large k. Our results are at odds with some other experiments performed on similar multi-scale grids, where significantly higher energy decay exponents and turbulence levels have been reported.

JFM classification

Turbulent Flows: Homogeneous turbulence Turbulent Flows: Turbulence theory Mixing: Turbulent mixing
Type
Papers
Information
Journal of Fluid Mechanics , Volume 680 , 10 August 2011 , pp. 417 - 434
Copyright
Copyright © Cambridge University Press 2011

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References

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